The EB virus infects umbilical cord blood lymphocyte or peripheral blood lymphocyte to transform the cells. However, the EB virus generally infects cells to remain merely latent, so the infected cells hardly produce mature viruses. Although B lymphocyte cell strains (BJAR, Ramos, etc.) uninfected with the EB virus can be infected with the EB virus to continuously carry it, such strains cannot produce a large amount of EB virus (Fields, B. N. and D. M. Knipe (ed.), 1990, Virology, 2nd ed. Raven press, New York: Chapter 68, Epstein-Barr Virus, Biology, pathogenesis, and medical aspects, G. Miller, pp. 1921-1957).
Cells such as Akata, B95-8, P3HR1, etc., are known as EB virus-producing cells. In particular, Akata cells treated with anti-human immunoglobulin antibodies produce a large amount of EB virus (Takada K, Int. J. Cancer, 33, 27-32 (1984) and Takada, K. and Ono Y, J. Virol. 63, 445-449 (1989)). However, these cells are those already infected with the EB virus, and merely produce the EB virus that has already infected, and there is no report on the use of these cells to effectively separate and multiply extracellular EB viruses.
In addition, there are reports on investigations into the separation and multiplication of EB virus by means of BJAB, BL30, BL41 and Loukes, i.e. EB virus-negative B-lymphocyte cancer cells (A. Marchini, R. Longnecker and E. Kieff, J. Virol. 66, 4972-4981 (Aug. 1992)). For production of EB virus, however, these cells should be induced with a chemical substance such as 5-AZACYTIDINE, 12-O-tetradecanoylphorbol-13-acetate (TPA) etc. or with a special plasmid (pSVNaeZ), so that there are problems such as the harmful influence (safety) of the chemical substance on the human body, the poor efficiency of plasmid induction, etc., and such a cell strain for separation and multiplication of EB virus is not satisfactory in respect of the separated and multiplied viral amount.